Re: Fastest airliner ?

From:         shevell@leland.stanford.edu (Richard Shevell)
Organization: Stanford University, Dept. of Aero/Astro
Date:         30 Jul 95 13:02:08 
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In article <airliners.1995.1134@ohare.Chicago.COM>, kls@ohare.Chicago.COM
(Karl Swartz) wrote:

> >Could anyone tell me what the fastest reported speed is for an
> >airliner till now ? (Could you express this speed in mph or km/hr
> >instead of Mach numbers..?)

> The Convair 990A Coronado was one of the fastest subsonic jetliners.
> The 747SP, which is slightly faster than the other 747 models, is the
> only jetliner I can think of which matches or at least comes close to
> the Coronado -- it cruises at about 645 mph, I believe.

The 747SP cruise speed is much less than stated above.  The 747SP being a
lighter airplane with the original large wing certainly cruises at or above
35,000 ft.  The speed of sound at that altitude is 660 mph.  Thus 645 mph
would be a Mach number of 0.977.  The never exceed Mach No. for the 747SP
is 0.92 and the cruise speed is significantly less.  Jane's (1989) gives
the max level flight speed at 30,000 ft.(inefficiently low altiude, higher
speed of sound) as 619 mph. and this is max thrust not the normal cruise
speed.  Assuming a cruise Mach No. of 0.87, (the probable maximum) at the
normal cruise altitudes the speed would be 574 mph.  Stretching to 0.88
would give 581 mph.

I do not think the Coronado was that fast.  It gained a higher drag
divergence Mach No. through the use of Whitcomb bumps, carefully shaped
bodies placed aft on the wing.  While the 'bumps' raised the Mach No. for
sharp drag increase, they added so much parasite drag that they did not
increase range and were never used again.  The Convair 990 was not a
successful airplane.

Transport speed data published in the press are often exaggerated by the
manufacturers who list maximum level flight speeds occurring at lower,
inefficient altitudes, with higher speeds of sound, and max thrust which
push he airplane up the drag divergence curve, a procedure never used by an
airline because of sharply higher fuel consumption.

Richard Shevell
Email: shevell@leland.stanford.edu